Electrochemical cells such as fuel cells and metal-air batteries, which use gas in an electrode reaction, are provided with a conductive porous layer to improve the battery performance thereof.
For example, a membrane-electrode assembly (MEA) that is used as a component of a solid polymer fuel cell has a structure wherein a conductive porous layer, a catalyst layer, an ion-conductive solid polymer electrolyte membrane, a catalyst layer, and a conductive porous layer are sequentially laminated.
Generally, a conductive porous substrate, such as carbon paper or carbon cloth, is used for this conductive porous layer. Further, to improve the conductivity, gas diffusivity, water drainability, etc., of the conductive porous substrate, a conductive layer comprising conductive carbon particles, water-repellent resin, etc., may be formed on the conductive porous substrate.
Conventional conductive porous layers are formed by applying a conductive layer-forming paste composition to a conductive porous substrate having a surface roughness of about tens of μm, such as carbon paper or carbon cloth, and then drying (application methods; see Patent Literature (PTL) 1 and 2). Therefore, due to the penetration of the paste composition into the conductive porous substrate surface, etc., it was difficult to form a conductive layer with a uniform thickness. When the film thickness of the conductive layer is not uniform as described above, that is, when there is variation in the film thickness of the conductive layer, stable permeation and diffusion of gas over the adjacent catalyst layer surface is impossible, which lowers fuel cell performance. Another method for producing a conductive porous layer comprises forming a conductive layer on a transfer film by a transfer method, then pressure-welding the conductive layer onto the conductive porous substrate, and removing the transfer film. However, compared to the above application methods, this method is insufficient in terms of adhesion between the conductive porous substrate and the conductive layer. Thus, there is room for improvement in battery performance, etc. The above problem is not limited to solid polymer fuel cells, but is also common among metal-air batteries, and the like.